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      <title>在TCP协议中，缓存机制有什么作用？为什么需要缓存？ - 交互式测验</title>
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              <h1>在TCP协议中，缓存机制有什么作用？为什么需要缓存？ - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
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  {
    "question": "根据文档，当TCP发送方的数据包在网络中丢失时，缓存机制如何确保数据的可靠传输？",
    "options": [
      "接收端缓存会主动重新请求丢失的数据包。",
      "发送端将未被确认的数据包保留在缓存中，以便在需要时进行重传。",
      "网络中的路由器会利用缓存恢复丢失的数据包。",
      "发送端缓存会自动丢弃所有后续数据包，直到丢失的包被找到。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "为了实现可靠性，TCP的发送端会把已经发送但尚未收到接收端确认（ACK）的数据包存储在自己的缓存（也称为重传缓冲区）中。如果在一定时间内没有收到确认，或者收到了重复的确认，发送端就会从缓存中取出相应的数据包进行重传，从而保证了即使在网络不稳定的情况下数据也能最终送达。",
    "source": "文档中「3. 可靠性保证 - 数据重传」部分",
    "hint": "思考一下，如果一个包裹寄丢了，应该是谁负责重新寄送？文档中提到了“当发送的数据包在网络中丢失或损坏时...”"
  },
  {
    "question": "文档中提到，发送端将多个小数据块聚合到缓存中再统一发送，这种做法主要带来了什么好处？",
    "options": [
      "可以显著提高网络的最大传输单元（MTU）。",
      "通过减少系统调用次数和网络往返次数来提升效率。",
      "确保了每个小数据块都能被独立加密，增强了安全性。",
      "降低了接收端处理数据的难度。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "频繁地为每一个小数据块进行系统调用和网络传输会产生巨大的开销。通过将它们先暂存在缓存中，然后一次性批量发送，可以有效合并多次操作为一次，从而减少了CPU的系统调用开销和网络传输的往返延迟，显著提高了数据传输的整体效率和系统性能。",
    "source": "文档中「1. 数据传输优化」部分",
    "hint": "文档中提到这种方式可以“减少频繁的I/O操作”和“降低CPU的开销”。"
  },
  {
    "question": "TCP协议利用缓存和窗口机制实现流量控制，其在接收端的主要目的是什么？",
    "options": [
      "加快应用层从缓存中读取数据的速度。",
      "防止因发送速率过快导致接收端缓冲区溢出而丢包。",
      "对接收到的数据进行实时压缩以节省存储空间。",
      "检测并丢弃所有重复的数据包。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "流量控制的核心是协调发送方和接收方的速率。接收端有一个大小有限的缓存区，如果发送方发送数据的速度超过了接收方应用层处理数据的速度，缓存区就会被填满，后续到达的数据包将无处存放而被丢弃。通过滑动窗口协议，接收方可以告知发送方自己还有多少可用的缓存空间，从而让发送方调整发送速率，避免数据丢失。",
    "source": "文档中「5. 实现TCP协议功能 - 流量控制」部分",
    "hint": "思考一下为什么需要“控制”流量？文档提到要“确保数据不会超出接收端的处理能力”。"
  },
  {
    "question": "当接收端收到的TCP数据包顺序错乱时，缓存扮演了什么关键角色？",
    "options": [
      "缓存会立即丢弃所有乱序的数据包。",
      "缓存会通知发送端立即重传所有数据。",
      "缓存会临时存储这些乱序的包，并根据序号进行重组，以保证应用层获得有序的数据流。",
      "缓存会将数据包直接按到达顺序交给应用层，由应用层负责排序。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "TCP协议承诺向应用层提供一个可靠、有序的字节流。由于网络传输的复杂性，数据包到达接收端的顺序可能与其发送顺序不一致。接收端的缓存会根据每个TCP段的序列号，将这些乱序到达的数据包先存储起来，然后像拼图一样将它们重新排列组合，直到形成一个连续的数据序列后，再交付给上层应用。",
    "source": "文档中「3. 可靠性保证 - 顺序保证」部分",
    "hint": "TCP协议的一个重要特性是保证数据的顺序。文档描述了接收端如何“重组完整的数据流”。"
  },
  {
    "question": "TCP进行数据分段的根本原因是什么？它与缓存有什么关系？",
    "options": [
      "为了并行发送数据以提高速度；缓存用于存储这些并行的数据流。",
      "为了适应网络的最大传输单元（MTU）限制；缓存用于在发送端暂存分段和在接收端进行组装。",
      "为了便于对小数据块进行错误校验；缓存用于存放校验失败的段。",
      "为了动态调整数据包大小以适应网络拥塞；缓存决定了数据包可以调整的范围。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "数据链路层（如以太网）对一次能够传输的数据帧大小有限制，这个限制被称为最大传输单元（MTU）。为了传输一个大于MTU的数据块，TCP必须在发送前将其分割成多个小于或等于MTU的小块（段）。发送端的缓存用于存放这些待发送的段，而接收端的缓存则用于收集这些分段，直到可以重新组装成原始的完整数据。",
    "source": "文档中「4. 数据流的分段与组装 - 数据分段」部分",
    "hint": "文档中明确指出了分段与一个叫做“MTU”的限制有关。"
  },
  {
    "question": "根据文档，除了流量控制，TCP的缓存机制还为哪一个重要的网络控制算法提供了基础支持？",
    "options": [
      "路由选择算法（如OSPF）。",
      "数据加密算法（如AES）。",
      "拥塞控制算法（如慢启动）。",
      "域名解析算法（DNS）。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "拥塞控制是TCP用于防止整个网络过载的核心机制。它通过探测网络的拥塞程度来动态调整发送数据的速率。这个过程严重依赖于发送和接收端的缓存。例如，发送方需要根据网络状况（如丢包）来决定是增加还是减少发送窗口的大小，而这一切的调整和数据的暂存都离不开缓存的支持。",
    "source": "文档中「5. 实现TCP协议功能 - 拥塞控制」部分",
    "hint": "在文档的最后一个部分，提到了缓存支持的两个核心功能，一个是流量控制，另一个是什么？"
  }
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                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  